This invention relates to preparation of diaminodiphenyl ethers, and more particularly to preparation of bis(aminophenyl) ethers (e.g. oxydianiline, hereinafter sometimes referred to as ODA).
Various bis(aminophenyl) ethers (hereinafter sometimes referred to collectively as BAPE's ) are known to be valuable as bifunctional cross-linking and network-extending agents for polymeric resins, plastics and elastomers. There is a substantial demand by users of BAPE's for high-purity and substantially colorless commercial grade of BAPE products, especially such ODA products.
In Canadian Pat. No. 992,991 (incorporated herein by reference), Jamieson et al. describe and claim inter alia a process for preparing 4,4'-diaminodiphenyl ether (also known as 4,4'-oxydianiline or simply 4,4'-ODA) which comprises refluxing a mixture containing approximately equimolar amounts of p-aminophenol, p-chloronitrobenzene, and potassium carbonate in dimethylformamide, hydrogenating the resulting mixture in the presence of a catalyst, recovering the dimethylformamide (or DMF as it is commonly referred to) by distillation, and crystallizing 4,4'-diaminodiphenyl ether (i.e., 4,4'-ODA) from the residue. As described in Example 1 of the Canadian Patent, the residue (remaining after distilling to recover 80% of the DMF) was "drowned with water, filtered and reprecipitated" to give "crude 4,4'-oxydianiline" (4,4'-ODA). Example 3 of Jamieson et al. states that, after "cooling and removal of catalyst by filtration, 4,4'-ODA was isolated as a pink solid by drowning the reaction mixture, including the DMF, with water and filtering," the pink solid having melting point (m.p.) of 187.degree.-189.degree. C. As described in each of Examples 1-3 of the Canadian patent, recovery (i.e., crystallization or isolation) of the 4,4'-ODA product includes a step of drowning with water. In Example 4 Jamieson et al. teach that the 4,4'-ODA "was isolated in the usual way," excess p-aminophenol was removed, the resulting "light pink product" had "m.p. 188.degree.-190.degree. C.," and "reprecipitation from n-butanol gave a nearly colorless product, m.p. 190.degree.-191.degree. C.,"
Although the Jamieson et al. process for preparing 4,4'-ODA represents a substantial advance, there remains a substantial need in the art for an improved process for preparing 4,4'-ODA (and other bis(aminophenyl)ethers). There also remains a need for an improved process for making BAPE's, especially ODA, having high purity and/or better color properties.